p.s. Facebook have this for years.

this is how to opt out:

https://www.facebook.com/settings?tab=ads&section=social&vie...

(select "Pair my social actions with ads for - No one")

Article about it:

http://www.forbes.com/sites/anthonykosner/2013/01/21/faceboo...

There were several HN posts on this as well will update once I find them...